Extensometric sensor for measuring the stresses acting on a drilling element and a device for mounting such a sensor

Abstract

An extensometric sensor for measuring stresses acting on a drilling element at a bottom of a well, with the sensor including a first measurement zone formed from at least two traction blades, on which are mounted measurement gauges, connected at their ends by uprights so as to form a first deformable parallelogram, with the traction blades being oriented in a first direction. A second measurement zone is formed of at least two torsion blades, on which are mounted measurement gauges, connected by cross pieces so as to form a second deformable parallelogram, with the torsion blades being oriented in a second direction perpendicular to the first direction. The first and second zones are connected and the same is mounted on a drilling element, with the cross pieces and uprights having large dimensions with respect to the torsion blades and the traction blades.

What is claimed is: 
     
       1. An extensometric sensor for measuring stresses acting on a drilling element at the bottom of a well by gauges, the sensor comprising: a first measurement zone formed from at least two traction blades having measurement gauges mounted thereon, said two traction blades being connected at respective ends thereof by uprights so as to form a first deformable parallelogram, said traction blades being oriented in a first direction;   a second measurement zone formed of at least two torsion blades having measurement gauges mounted thereon, said two torsion blades being connected at respective ends thereof by cross-pieces so as to form a second deformable parallelogram, said torsion blades being oriented in a second direction perpendicular to the first direction;   means for connecting said first zone and said second zone together; and   means for mounting the extensometric sensor on said drilling element, and   wherein said cross-pieces and said uprights have a larger cross-sectional dimension with respect to said torsion blades and said traction blades.   
     
     
       2. The extensometric stress measurement sensor as claimed in claim 1, wherein said means for connecting comprises an articulation disposed centrally with respect to a longitudinal axis passing through said first and second zones, said articulation providing for flexion of the sensor along said longitudinal axis without any action of deformation on the first and second zones. 
     
     
       3. The extensometric stress measurement sensor as claimed in claim 2, wherein said uprights of the first zone each comprise at one end thereof a right-angled extension, wherein an extension of a first upright is connected to the flexion articulation, and wherein said means for mounting includes a lug provided on an extension of the second upright for mounting the sensor to said drilling element. 
     
     
       4. The extensometric stress measurement sensor as claimed in claim 3, wherein a first cross-piece of said second zone is connected to the flexion articulation, and wherein said means for mounting includes a lug provided on a second cross-piece for mounting the sensor to the drilling element. 
     
     
       5. The extensometric stress measurement sensor as claimed in claim 4, wherein extensions of said uprights and extensions of said cross pieces are disposed in parallel directions and perpendicular to the direction of the flexion articulation. 
     
     
       6. The extensometric stress measurement sensor as claimed in claim 5, wherein each of said first and second measurement zones comprises three blades, two of said three blades form opposite faces of the deformable parallelogram and the third blade is disposed between the first two blades and supports the stress measurement gauges. 
     
     
       7. The extensometric stress measurement sensor as claimed in claim 6, wherein a ratio between a length of the blades and a total length of the sensor is between 1/10 and 2/10, and wherein a ratio between a thickness of said blades and a thickness of the uprights or of the cross-pieces is between 1/20 and 1/10. 
     
     
       8. The extensometric stress measurement sensor as claimed in one of claims 1 or 2, mounted on a drilling element at the bottom of a well, wherein said means for mounting includes support means for supporting said sensor so that an axis of said sensor is disposed substantially in a longitudinal direction of said drilling element. 
     
     
       9. The extensometric stress measurement sensor as claimed in claim 8, wherein said support means comprise two support rings disposed about the drilling element and each respectively supporting an end of the sensor through a fixing lug and a member disposed symmetrically to said sensor with respect to the axis of the drilling element. 
     
     
       10. The extensometric stress measurement sensor as claimed in claim 9, wherein said member disposed symmetrically to the sensor is formed by a second extensometric sensor. 
     
     
       11. The extensometric stress measurement sensor as claimed in claim 10, wherein each of the support rings comprises two projections diametrically oppositely disposed with respect to the axis of the drilling element and disposed in a direction perpendicular to the direction of the fixing lug said projections forming points for mounting said rings on said drilling element by securing means. 
     
     
       12. The extensometric stress measurement sensor as claimed in claim 11, wherein said projections each comprise a flexible blade forming an articulation for the support rings with respect to the drilling element when said drilling element is subjected to a flexion force in a plane containing said projections. 
     
     
       13. The extensometric stress measurement sensor as claimed in claim 12, wherein said support rings comprise recesses for engagingly receiving the fixing lugs, and wherein said fixing lugs are held in position in said recesses by locking screws 
     
     
       14. The extensometric stress measurement sensor as claimed in claim 13, wherein said support rings further comprise lateral recesses, situated symmetrically with respect to the recess receiving the fixing lug, in which are engaged wedges which are movable by pusher screws so as to prestress the sensors. 
     
     
       15. The extensometric stress measurement sensor as claimed in claim 14, wherein damping shoes are placed between the sensors and the drilling element for damping vibrations. 
     
     
       16. The extensometric stress measurement sensor as claimed in claim 2, wherein a first cross-piece of said second zone is connected to the flexion articulation and a second cross-piece is provided with a lug for fixing to said drilling element. 
     
     
       17. A method for measuring a tension and twisting moment applied to a drilling element the method comprising the steps of: providing an extensometric sensor including a first measuring zone and a second measuring zone, said first measuring zone including a central traction blade and an additional traction blade on opposite sides of said central traction blade, said traction blades being connected to form a first deformable parallelogram, said second measuring zone including a central torsion blade and an additional torsion blade disposed on respective sides of said central torsion blade, said torsion blades being connected to form a second deformable parallelogram;   mounting said extensometric sensor on the drilling element so that an axis of the extensometric sensor is disposed substantially in a longitudinal direction of said drilling element;   placing stress gauges on the central traction blade and the central torsion blade;   measuring generated deformations by said stress gauges in said first measuring zone and said second measuring zone;   providing an output signal from each of the stress gauges of measured deformations in said first measuring zone and said second measuring zone; and   calculating stresses applied to the drilling element by summing the output signals from the stress gauges in the first measuring zone so as to obtain a value of the tension and summing the output signals from the stress gauges in the second measuring zone so as to obtain a value of the twisting moment.